4.	Cash, Cash Equivalents and Marketable Securities

Cash equivalents and marketable securities as of December 31, 2014, and 2013 consist of the following (in thousands):

	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
December 31, 2014
Cash and cash equivalents:
Cash	$	2,522	$	-	$	-		$	2,522
Money market funds		46,989		-		-			46,989
Total cash and cash equivalents		49,511		-		-			49,511
Marketable securities available-for-sale:
U.S. government agency securities		73,140		11		(10	)		73,141
Total marketable securities available-for-sale		73,140		11		(10	)		73,141
Total cash, cash equivalents and marketable securities	$	122,651	$	11	$	(10	)	$	122,652
December 31, 2013
Cash and cash equivalents:
Cash	$	1,766	$	-	$	-		$	1,766
Money market funds		20,013		-		-			20,013
U.S. government agency securities		1,343		-		-			1,343
Total cash and cash equivalents		23,122		-		-			23,122
Marketable securities available-for-sale:
U.S. government agency securities		166,285		16		(47	)		166,254
Total marketable securities available-for-sale		166,285		16		(47	)		166,254
Total cash, cash equivalents and marketable securities	$	189,407	$	16	$	(47	)	$	189,376

The maturities of our marketable securities available-for-sale are as follows (in thousands):

	December 31, 2014
	Amortized Cost		Estimated Fair Value
Mature in one year or less	$	72,390	$	72,391
Mature after one year through two years		750		750
	$	73,140	$	73,141

There were no realized gains or losses from the sale of marketable securities in the years ended December 31, 2014, 2013 and 2012. All of our investments are classified as short-term and available-for-sale, as we may not hold our investments until maturity.